abstract

Fitness-For-Service (FFS) assessment procedure can be also used to determine a reduced Maximum Allowable Working Pressure (MAWP) for cylindrical and spherical pressure vessel with local metal loss. A reduced MAWP is calculated from the Remaining Strength Factor (RSF). RSF is defined as ratio between plastic collapse load of the damaged component and that of the undamaged component. RSF needs to be calculated accurately in order to continue the damaged component in service safely. In this paper, RSFs of the damaged components with variously-shaped local metal loss were investigated. Especially, effects of circumferential width of local metal loss for cylindrical pressure vessel are investigated by both hydrostatic burst test and finite element analysis (FEA). The configurations of the local metal loss are rectangle. The longitudinal length and minimum thickness are fixed. FEA using the criterion proposed by Miyazaki et al. is effective to estimate fracture ductility under the multi-axial stress condition accurately, and effects of circumferential width is evaluated. In addition, RSF for spherical pressure vessel with relatively large diameter/thickness ratio was calculated by finite element analysis. Both results were compared to the calculation results using the equation in API 579-1/ASME FFS-1. The FFS assessment procedure is validated as conservative assessment experimentally and numerically.

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